1. Field of the Invention
The invention disclosed and taught herein relates generally to tools for reaming subterranean wellbores; and more specifically relates to reamer tools having a combination of rolling and fixed cutters and related methods.
2. Description of the Related Art
Drill bits used in drilling of subterranean wellbores typically comprise fixed cutter bits or rolling cutter bits. Rolling cutter bits typically include a body having legs extending downward and a head bearing extending from the leg towards the axis of the bit body. Frusto-conically shaped rolling cutters are rotatably mounted on each of these journals and are included with cutting teeth on the outer surface of these cones. As the bit rotates, the cones rotate to cause the cutting elements to disintegrate the earth formation.
In some situations, a pilot reamer drilling system is employed where two or more bits are combined on a single drill string. Here, the lowermost bit, commonly referred to as a pilot bit, creates a pilot hole and an upper earth boring bit enlarges the pilot hole diameter. The bit enlarging the hole diameter is referred to as a reamer. Typically, the pilot bit comprises a conventional bit, i.e., either a rolling cutter bit or a fixed cutter bit. The reamer bit usually employs rolling cutters as cutting members that are attached to the reamer body. Pilot reamer drilling systems are used to drill large diameter boreholes that may require enhanced stabilization. For example, U.S. Pat. No. 6,386,302 to Beaton discloses a “reamer for drilling a hole having a diameter larger than a pass through diameter [and] in one aspect includes a body having reaming blades affixed at azimuthally spaced apart locations.” As another example, U.S. Pat. No. 7,416,036 to Forstner et al., which is assigned to the assignee of the present invention and incorporated herein by reference for all purposes, discloses a “BHA compris[ing] a pilot bit and a reamer above it that is larger in diameter than the suspended liner.” As other examples, U.S. Pat. Appl. Pub. No. 2009/0218140 to Pessier et al. discloses a reamer bit comprising “four cutter mounts [with] rolling cutters on each mount” and U.S. Pat. Appl. Pub. No. 2009/0166093 to Pessier et al. discloses a reamer bit having rolling cutters and stabilizer pads on the body, each of which is assigned to the assignee of the present invention and incorporated herein by reference for all purposes. Although each of these bits may be workable for certain limited applications, an improved hybrid reamer with enhanced reaming performance is desirable.
The invention disclosed and taught herein is directed to an improved tool having a hybrid reaming section for reaming a wellbore and to methods of making and using the improved tool.